1. Field of the Invention
This invention relates to a signal generating system and more particularly to a system and apparatus for generating electrical signals having the waveform of specific musical instruments and having a cathode ray tube with a target as the basic signal generating means.
2. Description of the Prior Art
Electronic simulation of complex musical waveforms of certain musical instruments, such as air driven organ pipes, has been achieved but presents a difficult technical problem. The difficulty is increased when an electronic organ is provided with stops to cause the generated sound signals to resemble those of other musical instruments, such as pianos, flutes, horns, etc.
Heretofore, electronic sound signals have been accomplished, with varying degrees of success, by synthesis of a complex electronic wave that supposedly resembles the desired tonal qualities of selected musical instruments. Electronic synthesis involves the use of oscillators to produce all of the necessary fundamental frequencies and the required harmonics in as close as approximation as possible to the harmonic content of the sound wave that is to be simulated.
The use of oscillators has a number of difficulties including, especially, the large number of oscillators required to produce all of the necessary musical notes. The oscillators must be extremely stable since a slight drift in one or more of the oscillators may considerably reduce the realism of the sound wave produced from the complex electronic waveform generated by the various oscillator signals.
In other sound generators used in prior art electronic organs, oscillators had been combined with frequency dividers to produce square waves with the proper fundamental frequency and with the necessary multiples thereof. The fundamental and frequency multiple square waves are combined, or synthesized, in desired ratios and are passed through a tone filter to remove undesired frequency spectral components. In general, the direct keying system is used for intermittently interrupting the square wave trains with the above harmonic series. However, a large number of filters is required to provide a desired ratio for the harmonic components to produce timbres. As a result conventional electronic organs are complicated in their construction.